Currently, an LTE system supports only carrier aggregation that is within a same station, and in this carrier aggregation scenario, one radio bearer corresponds to one packet data convergence protocol(PDCP) entity and one radio link control(RLC) entity. To increase application scenarios of carrier aggregation, inter-station carrier aggregation is put forward. A difference of inter-station carrier aggregation from intra-station carrier aggregation includes: A same radio bearer may correspond to one PDCP entity and multiple RLC entities, and moreover, on a network side, the multiple RLC entities may be separately located on different stations.
In this way, an original data transmission process applicable to intra-station carrier aggregation needs to be optimized.